Spore-forming, Desulfosporosinus-like sulphate-reducing bacteria from a shallow aquifer contaminated with gasolene

Previous studies on the geochemistry of a shallow unconfined aquifer contam inated with hydrocarbons suggested that the degradation of some hydrocarbon s was linked to bacterial sulphate reduction. There was attenuation of naph thalene, 1,3,5-trimethylbenzene (TMB), toluene, p-xylene and ethylbenzene i n the groundwater with concomitant loss of sulphate. Here, the recovery of eight strains of sulphate-reducing bacteria (SRB) from the contaminated sit e is reported. All were straight or curved rod-shaped cells which formed en dospores. Amplification and sequencing of the 16S rDNA indicated that the s trains were all sulphate reducers of the Gram-positive line of descent, and were most closely related to Desulfosporosinus (previously Desulfotomaculu m) orientis DSM 8344 (97-98.9% sequence similarity). The strains clustered in three phylogenetic groups based on 16S rRNA sequences. Whole cell fatty acid compositions were similar to those of D. orientis DSM 8344, and were c onsistent with previous studies of fatty acids in soil and groundwater from the site. Microcosms containing groundwater from this aquifer indicated a role for sulphate reduction in the degradation of [ring-UL-C-14]toluene, bu t not for the degradation of [UL-C-14]benzene which could also be degraded by the microcosms. Adding one of the strains that was isolated from the gro undwater (strain T2) to sulphate-enriched microcosms increased the rate of toluene degradation four- to 10-fold but had no effect on the rate of benze ne degradation. The addition of molybdate, an inhibitor of sulphate reducti on, to the groundwater samples decreased the rate of toluene mineralization . There was no evidence to support the mineralization of [UL-C-14]benzene, [ring-UL-C-14]toluene or unlabelled m-xylene, p-xylene, ethylbenzene, TMB o r naphthalene by any of the strains in pure culture. Growth of all the stra ins was completely inhibited by 100 mu mol l(-1) TMB.